Many products are irradiated using industrial irradiators such as electron beam (e-beam) sterilizers. Electron beam accelerators are used in a variety of applications such as pharmaceutical/medical device sterilization, food and cosmetic sanitization, industrial cross-linking and gem treatment. Industrial electron beam irradiators accelerate electrons through products such as pharmaceuticals, biologics, and medical devices as said products move in front of the radiation source (i.e. scan horn). The electron's kinetic energy is measured in electron volts. The radiation kinetic energy (electron volts), number of electrons accelerated and the time during which the product is exposed determines the amount of radiation, which is absorbed within the product.
The depth-dose profile within the product is directly tied to the kinetic energy spectrum. Not all parts of the product absorb the same amount of radiation since the energy accumulation can come from both direct (attenuation) and indirect (build-up) absorption of energy. Said absorption characteristics are heavily influenced by the kinetic energy of the accelerated electrons. Thus, the lowest level of radiation absorption within the depth-dose profile must be sufficient to sterilize (treat) the product while the highest radiation absorption within the depth-dose profile must not negatively impact the functionality of the product. This is especially important when the product includes biologic or active components that are sensitive to radiation absorption. Once a depth-dose profile is established for a given product, it is important to ensure that the profile does not vary beyond permissible limits.
Products may have components which are adversely affected by exposure to radiation above pre-determined levels (e.g., biologics) and variations in the radiation absorption applied to those products may greatly influence their functionality. Radiation absorption is a function of the radiation kinetic energy (e.g., electron-volts), number of electrons, movement in front of the radiation source, and the duration of application to the product at a specific depth within the product. Time (duration) is easy to measure. However, techniques known to directly measure electron kinetic-energy and related kinetic energy spectrum are labor intensive, expensive and have difficulty in diagnosing subtle changes in electron beam energy. These subtle changes may impact the depth dose profile of sensitive products (such as combination products and pharmaceuticals). Currently, technologies are not readily available to be utilized as a benchmark to diagnose changes in the electron beam energy. The current technologies available directly measure said energy.
The current mechanism for formal electron beam measurement is largely based on a human element to establish a tangent line based on the depth dose within the irradiation target or phantom. Subtle changes in the estimation of said tangent line can impact stated electron energy by a large margin. A device is necessary to verify and monitor electron beam energy, which is solely based on radiation physics, not a human interpretation of the data. Currently, automated systems are available to remove or reduce the human element, however, these systems are very expensive, take experience to utilize said systems, and are difficult to transport to an array of processing sites.
The current technology utilizes a very rough estimate of probable electron energy spectra and the design is built to measure said energy based on confluent layer(s) of dosimeter(s). Dosimeter placement is not tied to radiation physics but a confluent placement pattern to find the point in which energy is no longer deposited.
The current measurement of energy is performed very infrequently (monthly or quarterly) which can lead to process changes that could potentially impact the validated state of the process. A monitor, or comparator, design could be utilized during each and every processing event to ensure compliance to the original validation event ensuring the product's integrity.
There are numerous technologies available to measure the kinetic energy for electrons as per ISO/ASTM 51649, entitled “Standard Practice for Dosimetry in an Electron Beam Facility for Radiation Processing at Energies Between 300 keV and 25 MeV”. The methodology in ISO/ASTM 51649 requires numerous dosimetry measurements or requires the use of specialized film reading equipment and substantial investment of time and highly specialized skills are required; therefore, this measurement is performed on a very sparse basis. U.S. Pat. No. 5,464,978 to Kudo et al. details an electron energy spectrometer having an electron energy analyzer equipped with plural detectors including a reference detector, with the spectrometer having a hemispherical electrostatic energy analyzer.
The published standard ISO/ASTM 51649 describes the procedure for performing an energy measurement for e-beam systems. The procedure includes instructions for placing the measurement device on a conveyor and describes moving a phantom across a radiation source. The definition of R50 or half-value depth is defined as the depth in a homogeneous material at which the absorbed dose has decreased to 50% of its maximum value. The published standard ISO/ASTM 51649:2005 further describes two different types of energy measurement devices, referred to as a stack and a wedge. In conjunction with a film dosimetry system, the devices may be used to measure the depth dose distributions in a defined reference material. In addition to aluminum, low density materials such as polyethylene, polystyrene, graphite, polymethylmethacrylate (PMMA), and nylon may be used for the reference material. However, this methodology details how to calculate kinetic energy.
An article entitled “Investigation of dose reduction in neonatal radiography using specially designed phantoms and LiF:Mg,Cu,P TLDs”, The British Journal of Radiology, 76 (2003), 232-237, by L. Duggan, et al., details dose reduction techniques for neonates in the intensive care unit. Alterations in beam energy (kVp and filtration) and collimation were investigated using specially designed phantoms mimicking a 700 g and 2000 g neonate, and ultrasensitive LiF:Mg,Cu,P thermoluminescence dosimeters. Differences in entrance surface dose (ESD) and dose at depth (3 cm or 5 cm) were compared for two overlapping fields. The reference discloses a phantom for measuring the dose profile at the surface and at different depths.
U.S. Pat. No. 6,364,529 to Dawson details a phantom for dose verification for intensity-modulated radiation therapy, comprising: a base; a static block fixed on the base; a dynamic block mounted on the base in adjustably spaced relation to the static block; at least one film divider positioned on the base between the static and dynamic blocks; and a plurality of radiation dose detectors mounted in at least one of the static and dynamic blocks. The patent further details a quality assurance phantom for multiple dosimetric devices, comprising: a pair of blocks spaced from one another and being adapted to receive radio-sensitive film there between, the blocks each having a plurality of cavities therein; and a plurality of dosimeters interchangeably mountable in the cavities of the blocks for measuring radiation dosages, wherein the dosimeters include radiochromatic film or ready pack film. This reference discloses a quality assurance phantom for multiple dosimetric devices having a pair of blocks spaced from one another and being adapted to receive radio-sensitive film there between, the blocks each having multiple cavities for mounting different dosimeters for measuring radiation dosages.
U.S. Published Patent Publication No. 2004/0228435A1 to Russell details a phantom for dose verification in intensity-modulated radiation therapy, comprising: a base of substantially tissue-equivalent material; and a two-dimensional array of cavities formed in said base with each said cavity being configured and dimensioned to receive a radiation detector. The phantom includes a base, which contains a two-dimensional, rectangular array or matrix of cavities, each cavity is dimensioned and configured for having a radiation detector inserted therein. This reference discloses a phantom for dose verification for intensity-modulated radiation therapy having a base of substantially tissue-equivalent material and a two-dimensional array of cavities formed in the base with each the cavities being configured and dimensioned to receive a radiation detector.
U.S. Pat. No. 6,225,622 to Navarro details a dynamic radiation scanning system for detecting radiation dosimetry of a beam emitted along an axis from a radiotherapy treatment machine comprising: at least one dosimetry probe constructed and arranged to sense photons and electrons; a dynamic phantom body formed from a material having a density approximating that of the human body and having a plurality of recesses for receipt of one or more of said probes therein; a gantry mounting assembly rigidly attached to said radiotherapy machine for positioning of said phantom body; and a lead screw assembly rigidly affixed to said gantry for providing coplanar movement of the dynamic phantom within a plane perpendicular to the axis of radiation emission; whereby movement of the dynamic phantom through a series of locations is carried out at varying depths so as to provide sufficient data to determine variations in beam uniformity. The dynamic phantom contains a dosimetry probe, usually an ion chamber, which may be inserted in one of several recesses, which are positioned so as to enable the user to alter the depth of the dosimetry probe within the block.
An article entitled “Multi-dimensional dosimetric verification of stereotactic radiotherapy for uveal melanoma using radiochromic EBT film”, E. Sturtewagen et al., Z. Med. Phys. 18 (2008) 27-36, details a type of radiochromic film (Gafchromic EBT) for dosimetric verification with establishing a calibration curve by using films cut in squares of 2×2 cm2 and positioned at 5 cm depth in a solid water phantom and irradiated with different dose levels (0.5 and 5 Gy) in a 5×5 cm2 field at 6 MV.
Patent Publication No. WO 0039608 (A1) to Karger, et al., details a fixing device for dosimeter, device and method for monitoring dynamically produced spatial dose distribution. Specifically, a device for monitoring dynamically produced spatial dose distributions is provided with at least two dosimeters which are arranged on a fixing device in a defined spatial relation to one another. Said dosimeter, when mounted on an arm of a motor-driven water phantom, can be automatically positioned, their positions can be measured and saved and desired dose values can be calculated for each dosimeter.
U.S. Pat. No. 6,979,829 to Calvert et al. details determining the amount of absorbed dose during irradiation, for example during sterilization of a biological material, relating to devices and methods for determining the amount of energy absorbed during irradiation. This system utilizes alanine dosimetry however the invention is to measure absorbed radiation dose (kGy) under specified environments from −120° C. to ambient conditions.
U.S. Pat. No. 6,429,444 to Korenev et al. details real time monitoring of electron beam radiation dose and employs a processor which determines the absorbed dose of radiation absorbed by each of the first and second items, with each of the inductive detectors including a ferrite member, such as a ferrite ring. A plurality of coiled loops are mounted around a periphery of the ferrite ring.
U.S. Pat. No. 4,877,961 to McIntyre et al. details an in-line electron beam energy monitor and control, as related to charged particle accelerators and relates in particular to the energy monitoring and stabilization of charged particle beams from such accelerators without momentum analysis. A beam of charged particles is scattered by a thin foil and the flux is sampled.
An article entitled “Evaluation test of the energy monitoring device in industrial electron beam facilities”, Radiation Physics and Chemistry 78 (2009) 481-484 describes a device consisting of a thick-walled (10 mm) electrically grounded aluminum cage shaped in the form of a Faraday cap. Two aluminum collector plates of different thicknesses, depending on the electron energy to be measured, are inserted into the cage separated from each other by an air gap of 5 mm and electrically insulated from the cage by ceramic posts. When the energy monitoring device was under the beam, currents, I1 from the front plate and I2 from the backplate, can be measured simultaneously.
An article entitled “Evaluation of the depth-ratio and backscattering-factor methods in quality control measurements of electron beam energies”, Applied Radiation and Isotopes 63 (2005) 217-222 details estimating the beam energy by the use of a ratio of two depth ionization measurements instead of constructing the whole depth curve. The two depths are selected on the descending part of the depth ionization curve, and the ratio of these depth readings is then related to the beam energy.
An article entitled “Dosimetry procedures in electron processing”, by A. Kovacs et al., A.I.I.I Newsletter, No. 25, vol. 1-2, pp 242-251, 1992, describes use of an aluminum wedge for dosimetry of electron beam processing.
U.S. Pat. No. 7,780,352 to Fox et al., details a radiation beam quality detection method having a stepped thickness X-ray filter.
An article entitled A FULLY INTEGRATED 10 MeV ELECTRON BEAM STERILIZATION SYSTEM, by Allen et al., Radiat. Phys. Chem. Vol. 46, No. 4-6, pp. 457-460, 1995, describes penetration range measurement in an aluminum wedge.
An 11-Step, step wedge penetrometer made of aluminum used in quality assurance for medical xray applications and is available from Oprax Medical Company. The step wedge penetrometer is used for fog testing, mAs linearity, contrast vs. kVp.
U.S. Pat. No. 7,580,504 to Lang et al. details calibration devices and methods and employs a calibration phantom which includes a radioopaque step-wedge. A calibration device comprising a radioopaque material (e.g., copper or aluminum) having a stepped thickness is described. In certain embodiments, the step-wedge calibration device has equivalent bone area density coverage.